Mitral annular calcification (MAC) involves build-up of calcium in the mitral annulus, the fibro-muscular band which supports the mitral valve. The annulus aids in valve function, contracting in early systole (contraction phase) and bringing the valve leaflets together. In diastole (filling phase) it enlarges allowing blood to flow freely across the valve. Calcification stiffens the annulus and can extend onto the valve leaflets stiffening them. When severe, MAC impairs flow across the valve (mitral stenosis). This is characterized by a pressure gradient across the valve which can be detected by Doppler echocardiography (ultrasound).
Routine Doppler echocardiography is performed at rest when heart rates and flow across the mitral valve are low. Thus, even with severe MAC, there may only be a small pressure gradient present. However, with exercise these gradients can rise rapidly, leading to symptoms such as fatigue and shortness of breath.
MAC is associated with aging and is becoming more prevalent. Our hypothesis is that MAC is a common cause of shortness of breath with exertion. Further, the investigator believes this is under-appreciated because routine Doppler echocardiograms are done at rest. Therefore, the investigator will study adult subjects with moderate to severe MAC during bicycle exercise. Doppler echocardiography will be used to measure both the resting gradient across the mitral valve and changes with exercise. Symptoms will be measured by Borg Perceived Exertion scale.
If the research team is successful, the research team expects to demonstrate convincingly that this commonly encountered finding on Doppler echocardiography is an important cause of patient symptoms.
